In a power distribution system, electrical switchgear are typically employed to protect the system against abnormal conditions, such as power line fault conditions or irregular loading conditions. There are different types of switchgear for different applications. A first type of switchgear is a fault interrupter. Fault interrupters are configured to automatically open a power line upon the detection of a fault condition.
A second type of switchgear is a recloser. Reclosers are configured to respond to a fault condition by rapidly tripping open and then reclosing a power line a number of times, in accordance with a set of time-current curves. After a predetermined number of trip/reclose operations, the recloser will “lock-out” the power line, if the fault condition has not been cleared.
A breaker is a third type of switchgear. Breakers are similar to reclosers. However, they are generally capable of performing only a single open-close-open sequence, and the currents at which they interrupt current flow are significantly higher than those of reclosers.
A capacitor switch is a fourth type of switchgear. Capacitor switches are used for energizing and de-energizing capacitor banks. Capacitor banks are used for regulating the line current feeding a large load (e.g., an industrial load) when the load causes the line current to lag behind the line voltage. Upon activation, a capacitor bank pushes the line current back into phase with the line voltage, thereby boosting the power factor (i.e., the amount of power being delivered to the load). Capacitor switches generally perform only one open operation or one close operation at a time.
All switchgears include contacts, which come into proximity with one another during a closing operation and out of proximity with one another during an opening operation. Typically, one contact is stationary and one contact is movable. The movable contact moves towards the stationary contact during the closing operation and away from the stationary contact during the opening operation.
Generally, switchgears incorporate spring loaded mechanisms connected to an operating member to positively open or close the contacts. One such device that is commonly used is a simple toggle linkage. The primary function of these mechanisms is to minimize arcing between the contacts by very rapidly driving the contacts into their open or closed positions. Various applications may require the use of a number of spring loaded mechanisms with associated latches and linkages.
To prime these mechanical systems, either by compression or extension of the drive spring, an actuator is normally provided. For example, an actuator can be a solenoid, motor, hydraulic device, or voice coil. A voice coil actuator is a fast, powerful, and precise means for moving a load, such as a movable contact of a switchgear. The voice coil actuator uses a magnetic field and a coil winding to produce a force for driving the movable contact of the switchgear.
The major disadvantage of a voice coil actuator is that the voice coil has no inherent stable position when it is not powered. To overcome this, various mechanical means, such as over-toggle latches, have traditionally been used to keep the voice coil, and thus the switchgear contacts, in a stable position. These mechanical means have many disadvantages, including requiring extra energy to release the latch and being needlessly complex by requiring multiple movable parts.
Therefore, a need exists in the art for a simpler method and device for latching and releasing a voice coil actuator. A further need exists in the art for such a method and device to be energy-efficient.